双面静水压下含点阵增强柱和空腔的夹芯板水下声振计算方法研究

随着潜艇工作深度不断增加,含点阵增强柱和空腔的复合材料夹芯板因其高强度和声振性能可设计性强的优良特性逐渐被应用于外部壳体结构。为建立一种考虑双面静水压的含点阵增强柱和空腔的复合材料夹芯板水下声振计算方法,研究高潜深环境下双面高静水压对围壳等内部充水结构声振性能的影响,本研究利用多层次均质化等效方法将含增强柱和空腔的水下复合材料夹芯板芯层等效为正交各向异性材料,得到均质夹芯板模型,然后基于应变能密度相等将横向双面静水压等效为面内均布载荷,对基于LW理论模型的均质夹芯板的水下振动方程进行修正,进而提出了一种考虑双面静水压的含点阵增强柱和空腔的复合材料板水下声振计算方法。最后,利用数值计算方法对本研究方法的准确性进行了验证,结果表明理论解与数值解吻合较好。该方法可以较准确的预报双面静水压对含点阵增强柱和空腔的复合材料夹芯板声振性能的影响。     

用等效参数法研究含球形空腔弹性体的吸声性能

复合弹性材料已广泛应用于水声吸声材料中。本文研究的对象是含有球形空气空腔、以均匀粘弹性介质为基材的复合吸声结构。文中以散射理论和可变形粘弹性介质力学的基本理论为基础，建立了该复合结构的物理模型，引入了等效参数的概念来研究它的声学特性，并且分析了结构参数对其声学性能的影响。     

零泊松比蜂窝芯等效弹性模量研究EI北大核心CSCD

采用柔性悬臂梁模型和欧拉梁模型分别对零泊松比蜂窝芯斜壁板大变形条件下的弯曲变形和蜂窝芯横壁板小变形条件下的变形进行分析,推导出了零泊松比蜂窝芯面内等效弹性模量理论计算公式,并将理论计算结果和有限元仿真及力学模型实验进行对比分析。结果表明:理论计算公式正确、有效;零泊松比蜂窝芯大变形方向等效弹性模量具有明显的非线性特征;等效弹性模量的计算应根据受力方向及应变大小选择相应的计算公式进行计算;壁板之间的夹角θ对等效弹性模量的影响很大,零泊松比蜂窝结构参数可设计性较强。     

Z向点阵增强泡沫夹芯复合材料平压性能

设计了一种新型Z向点阵增强泡沫夹芯复合材料,以复合材料柱作为Z向点阵增强材料,并对不同分布密度Z向点阵增强材料的泡沫夹芯复合材料试验件进行了平压试验,探究了其平压力学性能和破坏方式。研究结果表明,当点阵间距为30 mm时,试样密度增加了2.8%,压缩强度和压缩模量分别提高了6.2倍和7.4倍。基于ABAQUS有限元软件建立了Z向点阵增强泡沫夹芯复合材料平压试验仿真模型,对其平压力学性能和破坏模式进行了模拟与分析。试验件平压强度有限元计算结果与试验结果偏差为10%左右,破坏方式与试验基本相同,验证了有限元模型的合理性和可靠性。     

蜂窝芯层等效参数研究综述

蜂窝芯层等效参数的相关研究是蜂窝夹层结构设计和计算的重要基础,深入研究蜂窝芯层的力学特性具有重要的应用意义。对蜂窝芯层等效参数的研究进行了综述,首先介绍蜂窝芯层面内等效参数的研究进展,主要基于经典梁理论和均匀化理论,从线性和非线性两方面展开综述。然后介绍芯层面外等效参数研究,围绕各种计算方法、等效力学模型、线性和非线性等效,以及各自的优缺点等问题进行总结和评述。此外还对一些解析公式的精度和适用范围进行了比较,以方便工程应用。最后,指出了这一领域需要进一步研究的若干问题。     

碳纤维增强金字塔点阵夹芯结构的抗压缩性能

提出了一种碳纤维增强复合材料点阵夹芯结构的一体化成型工艺方法。该方法克服了传统夹芯结构面板与芯子之间因需要二次粘接或焊接的方法所带来弱界面的缺点。将纤维杆两端埋入面板内,使面板与芯子成为一体而不存在明显的界面。对用该方法制备的碳纤维增强金字塔点阵夹芯板进行平压试验,研究发现随着载荷的增加,纤维杆发生弹性屈曲并在中间部位出现断裂。理论分析了点阵夹芯结构平压载荷下的弹性模量和纤维杆极限屈曲载荷。通过与传统夹芯材料相比较发现,这种新型复合材料点阵夹芯结构具有密度低、比强度和比刚度高等优点。      

曲面碳纤维增强树脂复合材料点阵夹芯结构的弯曲和振动特性

采用热压一次成型的工艺制备了曲面碳纤维增强树脂复合材料点阵夹芯结构,进行了三点弯试验探究了结构的弯曲破坏载荷与破坏模式。结果显示：结构的载荷位移曲线分为4个阶段,分别为线性阶段、损伤起始阶段、损伤演化阶段和失效阶段;破坏模式主要为面板压溃与节点失效。通过ABAQUS显示求解器建立了有效的弯曲和模态振动模型,得到弯曲破坏过程的失效模式、载荷位移曲线及结构振动模态与固有频率。讨论了不同参数(几何参数和材料性能)对弯曲和振动性能的影响,比较了不同边界条件对固有频率的影响。结果显示：相对密度(面板厚度、芯子直径)的增加会使结构的弯曲破坏载荷和固有频率增大,而芯子倾角ω的增大会使弯曲破坏载荷与固有频率的减小;材料的比刚度越大,固有频率越高。     

δ-Al2O3f/Al基复合材料弹性模量的有限元能量法预测

Based on the energy equivalence principle, the elastic modulus of δ-Al₂O_3f/Al composite was predicted by means of the Finite Element Method. In the predicting, the random orientation distribution of short fiber was considered. The results were compared with the experimental values and those of previous predicting methods. In the end, it can be concluded that the method developed in this paper is reasonable and precise.     

碳纤维增强环氧树脂复合材料金字塔点阵夹芯假脚结构在竖向载荷下的力学性能

对碳纤维增强树脂复合材料金字塔点阵夹芯假脚结构在竖向载荷下的力学性能进行研究.制备了三种不同相对密度的假脚,并进行了竖向载荷压缩试验.结果 表明,相对密度对结构力学性能的影响显著,载荷-位移曲线呈非线性,峰值载荷和刚度值随相对密度的增加而增大,三种相对密度的破坏模式均为节点的失效和面板的皱曲,结构具有一定的能量吸收能力...     

δ-Al2O(3f)/Al基复合材料弹性模量的有限元能量法预测

基于能量等效原理, 采用三维有限元方法, 考虑短纤维位向的随机分布对复合材料弹性模量的影响, 利用有限元能量法对δ-Al₂O_(3f)/Al 合金复合材料的弹性模量进行了预测。预测结果与实验结果和目前常用的几种预测方法进行了比较, 表明该方法是合理、准确的。     

考虑周期微结构分布特征的Mori-Tanaka方法

利用两点间应变Green函数张量概念所建立的应变场积分方程, 推导了两相复合材料中夹杂的应变集中张量。该张量较之传统Mori-Tanaka (MT)法采用的由稀疏法导出的应变集中张量, 增加了一个与夹杂体积分数和分布相关的项, 并由此发展了考虑周期微结构分布特征的MT法。传统的MT法虽然能很好地预测正六角形分布圆截面纤维增强复合材料等的有效模量, 但不能反映正方形分布时的四方对称性特征, 本文作者所发展的方法弥补了这方面的不足, 并且所预报的有效刚度和柔度仍然保持了原MT方法所具有的自洽特性。最后通过与双周期有限元计算结果的对照验证了本文方法的精度。      

A method to measure shearing modulus of the foamed core for sandwich plates

This paper reports on a test method to evaluate the shearing modulus of foamed core which is used for sandwich plates. Although this kind of relatively soft core is widely used for various applications, a suitable test method has not necessarily been established. In the present study, a symmetric test sample with four pieces of core is used to eliminate undesirable deformation due to eccentric load. By varying the core length and the core thickness, we found that the shearing modulus strongly depends on the specimen configuration. This tendency was also recognized from the results of FEM and beam theory analyses where the shearing deformation is incorporated. Finally we propose a methodology for obtaining a reliable shearing modulus with the aid of FEM analysis.     

高模碳纤维细观力学分析

将碳纤维视为由微晶和无定型碳所构成的二相复合材料,以Mori-Tanaka方法研究了碳纤维微观结构对弹性模量的影响。对四种高模碳纤维M35JB、M40JB、M46JB及M55JB的微观量进行了测量。微晶的长细比由XRD实验测得,碳纤维石墨化程度由拉曼光谱分析得到。影响碳纤维弹性模量的因素包括:微晶的长细比、体积分数及取向度。通过计算细观力学模型得到了四种高模碳纤维的微晶体积分数。研究发现:碳纤维石墨化程度越高,微晶体积分数越大。碳纤维弹性模量随着微晶取向度、体积分数和长细比的增加而增加,且对这三种因素做了比较,微晶取向度和体积分数对弹性模量的影响高于微晶长细比对弹性模量的影响,只有当微晶取向度接近100%时,其对弹性模量的影响才有可能被微晶长细比超越。微晶取向度和体积分数增加的最初阶段,取向度对弹性模量的影响较大,随着两影响因素的增加,取向度对弹性模量的影响最终被体积分数超越。     

A spectral alternating method for elastostatic problems with multiple spherical cavities

The problem of an infinite elastic solid containing an arbitrary number of non-overlapping spherical cavities of arbitrary sizes and locations and with arbitrary boundary tractions is considered. The numerical procedure to solve this boundary value problem is based on a spectral method in which the boundary displacements and tractions are represented by truncated series of surface spherical harmonics. By using an alternating method, the problem containing multiple spherical cavities is replaced by a sequence of problems for a single spherical cavity with the boundary conditions adjusted iteratively to account for the cavity interactions. A least squares approximation is used to determine the unknown coefficients of surface spherical harmonics representing these cavity interactions. Several examples are given to illustrate the approach. An erratum to this article can be found at     

声激励共振法测量微机械材料的杨氏模量

微机械材料的杨氏模量测量是随着微机械构件的产生而提出的一项新技术。文章综述了已有的测量微机械材料杨氏模量的方法。提出了用声激励共振法来测量微机械材料的杨氏模量。这种方法具有测试装置简单、测量容易、精度高等特点。     

Analysis of equivalent elastic modulus of asymmetrical honeycomb

In this report, elastic moduli of honeycomb consisting of asymmetrical hexagonal cells are studied by using a theoretical approach and the finite element method (FEM). Based on the change in the shape of the hexagonal cell, explicit equations describing the equivalent elastic moduli of honeycomb with cell wall parallel to the y-axis are proposed. In the analysis of honeycomb deformation, the shear deformation was considered in addition to bending deformation and tensile deformation. As a result, the equivalent elastic moduli could be calculated with extremely high precision.     

V-型皱褶芯材承压的均质化等效模型

采用代理模型获得V-型皱褶芯材等效屈服应力、等效平台应力和几何参数之间的关系,并据此提出了一种承受静力/准静力面外压缩的V-型皱褶芯材均质化等效模型。计算结果与试验结果的对比表明:皱褶芯材的均质化等效模型可以很好地模拟原结构的弹塑性力学特性,并能大大减少计算耗时。对于皱褶夹芯板在结构中,特别是抗坠毁吸能结构中的应用,本文的等效模型提供了一种高效率的计算及优化手段。     

Creep and relaxation functions of a heterogeneous viscoelastic porous medium using the Mori-Tanaka homogenization scheme and a discrete microscopic retardation spectrum

In this paper the macroscopic creep and relaxation functions of a heterogeneous viscoelastic porous medium are derived by using Mori-Tanaka homogenization scheme. Analytical and semi-analytical solutions can then be determined with a parametric number of heterogeneous phases embedded in a viscoelastic matrix whose behavior is described with a parametric number of analogical units. Under some simplifying assumptions, a solution strategy is presented in order to make explicit how the microscopic retardation and relaxation times of the viscoelastic matrix control the distribution of the retardation and relaxation times of the homogenized medium.     

A modification of the Mori-Tanaka estimate of average elastoplastic behavior of composites and polycrystals with interfacial debonding

A modification of the Mori-Tanaka method is proposed to evaluate the average elastoplastic behavior of composites and polycrystals in a virtual matrix. The virtual matrix is an elastic material in which real matrix material and inhomogeneities are embedded, and its volume vanishes as a limit after homogenization. With regard to elasticity, depending on the choice of material properties of this virtual matrix, many kinds of average moduli between the classical bounds can be predicted. In this paper, we extend the application of this method to elastoplastic materials. Furthermore, Weng’s approximate model of interfacial debonding between the inclusions and the matrix is installed, because of its very simple criterion for the initiation of debonding to simulate progressive debonding phenomena. Several numerical examples without interfacial debonding show the applicability of the virtual matrix concept to elastoplastic materials. The characteristics of the model and its overall behaviors are described through the use of typical numerical simulations with debondings. Finally, comparisons with experimental results including debondings demonstrate the eligibility of the proposed method and models, and the application of the present method to designing a hybrid FRP is overviewed.     

确定毛细管尺寸的当量方法研究

在类比法和当量法基础上，提出多根毛细管之间长度、内径相互转换的当量方法。指出毛细管的摩擦系数对当量转换公式有直接的影响。计算表明，当N／Neq=1．5时，采用不同毛细管摩擦阻力系数进行毛细管当量长度的计算结果差别在6％以内。以制热量为8．5kW和9．85kW的空调机组采用的毛细管为基准，通过类比方法和笔者提出的当量方法计算制热量18kW的空调机组应采用的毛细管的几何尺寸。实验表明：以8．5kW机组为基准时，毛细管内径和长度的计算值和实验值分别相差-7．2％和2．9％；以9．85kW机组为基准时，毛细管内径和长度的计算值和实验值分别相差-6．5％和12．7％。实验说明笔者提出的方法可以用来指导空调机组的毛细管匹配实验。